In the production of di(4-aminocyclohexyl)methane by the catalytic hydrogenation of di(4-aminophenyl)methane, essentially three stereoisomers are produced. ##STR1##
It is known in the art that in order to produce a corresponding isocyanate (via the known phosgenation process) which is liquid and storage stable at room temperature (i.e. from 20.degree. to 25.degree. C.), the mixture of amine stereoisomers used for phosgenation must contain the trans, trans stereoisomer in relatively narrow amounts (typically from 15 to 40 percent by weight, and preferably from 18.5 to 23.5 percent by weight).
Numerous techniques are known in the art for the production of amine mixtures containing the requisite amount of the trans, trans isomer. Typical of these known techniques are those described in U.S. Pat. Nos. 3,153,088; 3,155,724; 3,393,236; 3,644,522; 3,711,550 and 3,766,272. These known techniques generally require the separation of an amine mixture containing the requisite amount of the trans, trans isomer from an amine mixture formed after hydrogenation and containing around 50% by weight of the trans, trans isomer. Processes are known in the art for the production of a di(4-aminocyclohexyl)methane mixture containing the requisite amount of the trans, trans isomer directly from di(4-aminophenyl)methane without the need for an intermediate separation step (see e.g. U.S. Pat. No. 2,606,928). However, the rates of reaction are much too slow for commercial application.
Numerous processes are known in the art for the production of di(4-aminocyclohexyl)methane from di(4-aminophenyl)methane via catalytic hydrogenation using supported and unsupported ruthenium catalysts. Typical of these processes are those disclosed in U.S. Pat. Nos. 2,494,563; 2,606,924; 2,606,928; 2,606,925; 3,347,917; 3,676,495; 3,959,374; 3,743,677; 3,914,307; 3,825,586; 3,636,108 and 4,161,492. While some of these processes yield an amine mixture containing the trans, trans isomer in an amount necessary to allow for the production of an isocyanate which is liquid and storage stable at room temperature, the rates of reaction are much too slow for commercial use.
Ruthenium based catalysts have also been described as being useful in the hydrogenation of (a) polycycloaromatic polyamines formed from aniline and formaldehyde (see U.S. Pat. No. 4,226,737); (b) 2,4-bis(p-amino benzyl)aniline (see U.S. Pat. No. 3,557,180); (c) 2,4'-diaminodiphenylmethane (see (U.S. Pat. No. 3,590,002); and (d) tolylene diamine/formaldehyde condensates (see U.S. Pat. Nos. 3,330,850 and 3,361,814). However, none of these processes relate to the present problems, i.e., production of a di(4-aminocyclohexyl)methane containing the trans, trans stereoisomer in the amount required.
Finally, the use of a specific amorphous form of ruthenium oxide has been described for the production of di(4-aminocyclohexyl)methane from di(4-nitrophenyl)methane. (See e.g., U.S. Pat. No. 3,742,049).